World

North Korea is believed to have conducted a widely anticipated nuclear test Tuesday, following an earthquake that monitoring agencies around the globe said appeared to be unnatural.

The South Korean Defence Ministry, which raised its military alert level after the quake, said it was trying to determine whether it was a test. Nuclear blasts can create tremors but they are distinct from those caused by natural earthquakes.

A world nuclear test monitoring organization detected what it called an "unusual seismic event" in North Korea.

"The event shows clear explosion-like characteristics and its location is roughly congruent with the 2006 and 2009 DPRK nuclear tests," said Tibor Tóth, the executive secretary of the Comprehensive Nuclear Test Ban Treaty Organization. The DPRK refers to North Korea's formal name, the Democratic People's Republic of Korea.

"If confirmed as a nuclear test, this act would constitute a clear threat to international peace and security, and challenges efforts made to strengthen global nuclear disarmament and non-proliferation, in particular by ending nuclear testing," Tóth said.

Kim Min-seok, a South Korean Defence Ministry spokesman, told reporters that North Korea informed China and the United States of its plans to conduct a nuclear test. It was not clear when Pyongyang told Beijing and Washington.